The present invention relates to an X-ray microbeam generating method for various kinds of apparatuses using X-rays, and a device for practicing the same.
Apparatuses using X-rays are extensively used today. X-rays for such an application must be condensed to form a microbeam having a small beam size. Various kinds of technologies for condensing X-rays have been proposed in the past. For example, X-rays, issuing from an X-ray generator or X-ray source may be condensed to a focus position or virtual light source by an X-ray Fresnel zone plate playing the role of a condensing element. The Fresnel zone plate may be replaced with a mirror totally reflecting X-rays on the basis of the fact that X-rays having a refractive index smaller than 1 are totally reflected when incident to the surface of an object at an angle less than a critical angle. Japanese Patent Laid-Open Publication Nos. 62-15014 and 4-43998 each teaches an arrangement including an asymmetrical reflection type crystal collimator located on an input X-ray path and a mirror. X-rays from a false emission point defined by the crystal collimator and X-rays from the original emission point are reflected to the same point by asymmetrical X-ray diffraction. Further, an X-ray beam may have its cross-section restricted by a slit or a pin hole so as to produce a spatially restricted X-ray beam.
On the other hand, a solar slit or dynamic diffraction using the perfect crystal of X-rays has customarily been used to restrict the angular divergence of an X-ray beam. However, the solar slit scheme can restrict the divergence angle to the order of minutes at most, so that the resulting microbeam is too broad to be called a plane wave. As for the X-ray perfect crystal scheme, X-rays scarcely interacts with a substance, so that a great number of lattice planes join in diffraction. That is, a great number of reflected waves contribute to interference, implementing a noticeable interference effect. This further restricts the angular spread of the diffracted wave and allows, under diffraction conditions, angular divergence in the direction of scattering planes defined by the direction of input X-rays and the direction of diffracted X-rays to the order to seconds.
However, the condensation of X-rays and the restriction of the divergence angle of X-rays have customarily been effected independently of each other, failing to produce an X-ray microbeam having a restricted divergence angle. This is because condensation is not achievable without increasing the angular divergence and because the angular divergence cannot be reduced without increasing the spatial spread. Moreover, the spatial spread can be reduced by a condensing element only at the focal position; at the other positions, the beam size increases. Therefore, as the distance from the focal position increases, the microbeam spatially spreads by many figures due to angular divergence. That is, the microbeam cannot be used at positions other than the focal position.